Hello I'm very sorry about posting something very basic but I haven't been able to run my pol server yet and I must have forgotten something...
1.changed ip and checked for my router
2.changed client

but now i just don't understand why I get this error in start.log

Error reading configuration file config/multis.cfg:
No index record for MultiID 5000
Element: House 0x1388, found on line 378
Server Shutdown: read_multidefs
Execution aborted due to: Configuration file error

Does your POL.cfg point to the directory that has "multi.mul" in it? If so, try deleting your multi.cfg file and restarting POL to see if it will generate the correct one.